Thin film technology in the semiconductor industry requires thin deposition layers, increased step coverage and conformality, large production yields, and high productivity, as well as sophisticated technology and equipment for coating substrates used in the fabrication of various devices. For example, process control and uniform film deposition directly affect packing densities for memories that are available on a single chip or device. Thus, the decreasing dimensions of devices and the increasing density of integration in microelectronics circuits require greater uniformity and process control with respect to layer thickness.
Moreover, numerous applications, including electrodes for high dielectric capacitors, require highly conductive, oxidation-resistant films.
Various methods for depositing thin films of complex compounds, such as metal oxides, ferroelectrics or superconductors, are known in the art. Current technologies include physical vapor deposition (PVD), RF sputtering, spin coating processes, and chemical vapor deposition (CVD), with its well-known variation called rapid thermal chemical vapor deposition (RTCVD). These technologies, however, have some disadvantages. For example, the RF sputtering process yields poor conformality, while the spin deposition of thin films is a complex process, which generally involves two steps: an initial step of spinning a stabilized liquid source on a substrate usually performed in an open environment, which undesirably allows the liquid to absorb impurities and moisture from the environment; and a second drying step, during which evaporation of organic precursors from the liquid may leave damaging pores or holes in the thin film. Further, both CVD and RTCVD are flux-dependent processes requiring uniform substrate temperatures and uniform distribution of the chemical species in the process chamber.
Atomic Layer Deposition (ALD) is also a technique used to deposit various types of thin films, including metal and dielectric films. The ALD process is a technique in which deposition can be achieved one atomic elemental layer at a time. ALD offers numerous advantages over other methods, including low impurities content, low processing temperatures, ultra thin film deposition, excellent conformality, and superior thickness uniformity over large substrate areas. Moreover, ALD films make excellent barrier layers.
Many metal layers of Group VIII elements, such as platinum (Pt), palladium (Pd), iridium (Ir), ruthenium (Ru), rhodium (Rh) and osmium (Os) have suitable properties for various uses in integrated circuits, including as electrical contacts. Such layers are also suitable for use as barrier layers between the dielectric material and the silicon substrate in memory devices, such as ferroelectric memories, and even as the plate (i.e., electrode) itself in capacitors. In some applications, such as DRAM circuits, the electrodes in the cell capacitor must protect the dielectric layer from interaction with surrounding materials, including interlayer dielectrics, and from the harsh thermal processing encountered in subsequent processing steps. Moreover, in order to function well as a bottom electrode, the electrode layer or layer stack must act as an effective barrier against oxygen and silicon diffusion. Oxidation of the underlying silicon will result in decreased series capacitance, thus degrading the cell capacitor. Oxidation also results in volume expansion which can lead to stress of parts.
There is thus a need for a thin film layer which overcomes or mitigates the above disadvantages. In particular, a highly conductive thin film is needed which has excellent diffusion barrier qualities, which is resistant to further oxidation and which can be deposited in a process which yields good conformality.